At present there are two types of chamfering machines the essential differences of which reside in the different possibilities of adjusting the guide foot which, in one case, has a fixed positioning adjustable by hand, while the other case can take a certain number of predetermined positions.
However, the two types mentioned above are based upon one common conception of the machine which is generally provided with a single motor suitable to carry out the transmission of all necessary motions. The moving members are the chuck to hold the blade, the grinder to sharpen the blade and the roller which carries out the feeding of the material to be chamfered carrying it to the cutting station.
In said machines it is also provided a clutch which allows the material feed roller to be disconnected in order to be able to change, within the limits allowed by the slip of the clutch, the rotation speed of the feed roller in connection with the speed of the blade and of the spring.
It is to be noted that in both types of chamfering machines the different members are located within an open box-shaped body which has to be fixed, with its opening turned downwardly, on a carrying plane disposed on top of a bearing framework.
In non automatic chamfering machines the guide or reference foot can be adjusted exclusively by hand. The foot is mounted on an adjustable support and can take any desired position owing to the presence of devices which are connected to adjustment handles; in this case, the foot is not provided with a next pitch. This means that once the position to be taken by the foot has been determined, the workpiece can be thinned according to one predetermined amplitude and angle only. If the angle or the chamfering depth have to be changed, as the piece for example needs two or more different workings, it is necessary to act manually each time on the adjustment handles in order to set the foot in the most suitable position.
On the contrary, in the so-called automatic chamfering machines or program machines different types of chamfering can be carried out as the foot can take different predetermined positions as to its height, slope and depth. Practically, owing to a mechanical device, the machine can be arranged to accomplish three different chamfers. In this case the foot is placed so that it is ready to perform a certain type of chamfer having a given slope, height and depth. When this foot programming has been carried out, acting on a mechanical selector operable by pedal or push-button, it is possible to change the foot position so that the latter can take one of the two other predetermined positions.
In this type of machines too the setting of the foot, within the graduation limits, can become continuous by previously interfering in the mechanical adjusting device. In other words, if chamfers having different features with respect to the ones obtainable by means of the three above mentioned settings are desired, it is necessary to act manually on mechanical setting devices by programming other foot positionings.
However these types of machines have many drawbacks.
A first drawback, connected to the mechanical basic conception of the machine, resides in the fact that the rotary cup-shaped blade, the feed roller to feed the piece to be chamfered and the grinder to sharpen the cup-shaped blade are mechanically interconnected, so that it is not possible to accomplish a variation in the motion of one of these members without varying the motion of the other members. This means that if the rotation speed of the cup-shaped blade has to be changed, the rotation speeds of the grinder and the feed roller are automatically changed. In order to prevent the latter speeds from changing it is necessary to interfere in the different members transmitting motion, for example it is necessary to miss some belts, to change ratios between gears or to carry out other similar operations, which involves a remarkable loss of time on the part of the operator and therefore a corresponding non use of the machine.
In chamfering machines in which the use of a clutch is provided in order to disconnect the movement of the feed roller from the movement of the cup-shaped blade and the grinder, it is possible to change, or in any case to rectify within a predetermined limit, the rotation speed of the feed roller with respect to the rotation speed of the other members mentioned above, letting the clutch conveniently slide. It is to be noted however that in this case the change of speed of the material to be fed appears approximate and difficult to set and it is always entrusted to the operator's personal evaluation.
Another drawback connected with the basic conception of known chamfering machines is that these machines must be very often submitted to maintenance; this is due to the wear of the clutch when it is envisaged, as it is continuously submitted to sliding in order to set the roller speed, and to the wear of some mechanical pieces which are submitted to an overstress or in any case to a stress non proportionate to their sizes which in present solutions must necessarily be reduced owing to lack of room.
Among these members it is necessary to remember the joint transmitting the movement from the motor shaft to the chuck carrying the cup-shaped blade. This joint must be of the extensible type so that, when it acts at its maximum elongation position, it is subject to vibrations which compromise its life, causing a quick wear of same, and giving rise to many problems as to the correct transmission of movement.
The mechanical unit which transmits the rotary motion to the unit destined to the feeding of the material is also subject to get easily and quickly worn. This unit, based on a worm screw-helical gear coupling, on one hand must necessarily have a small size due to lack of room, while on the other hand is submitted to continuous, wearing stopping and starting stresses originated from the fact that transmission occurs through a clutch.
Furthermore, the passage of movement through a plurality of members very small in themselves involves a big problem as to the accuracy of a work; in fact a small error brought by an upstream member becomes a bigger error when it reaches the members acting on the piece to be chamfered.
Further drawbacks are present in the guide feet, either in the case of feet having a single manual positioning, or in the case of feet having a multiple program positioning. In both cases the different positionings are accomplished by means of a series of controls resulting from cams, mechanical stops, levers and from a plurality of kinematic motions involving a great number of small sized components, which are obliged to work in a particularly heavy environment placed near the sharpening area of the blade. The material removed during the grinding such as emery and steel dust, lying in this area, damages the above mentioned components, which involves the necessity of a very frequent overhaul, cleaning and adjustment of same.
As to the chamfering machines provided with a programmable foot, it is to be noted that at present it is possible to program a rather restricted number of workings (three) on the machine, which is not sufficient to meet all the requirements of the modern production. Furthermore, once the three workings have been programmed, by suitably positioning the guide foot, it is possible to work only on the basis of the three programmed positions; if it is desired to accomplish a chamfering which is not contemplated by the program, it is necessary to interfere in this program, to carry out the chamfering which was not contemplated and to interfere again in the devices so that the machine can go back to its initial conditions. Obviously this involves a remarkable loss of time on the part of the operator and consequently a slackening of production.
It is also to be noted that in all the solutions hitherto known in the art it is not provided a detector suitable to detect the position of the fore cutting edge of the blade, while it is very important for the blade to keep a precise axial position, depending upon the material to take away. Actually, when it is necessary to pass from one material having particular features of thickness and hardness to another material of different features the operator, acting on the handles, must move forward or backward the blade edge till it reaches a suitable position; however this position is stated according to the operator's judgment and is not pointed out by any reference in the machine.
The blade wear due to sharpening operation is submitted to a similar check too. In fact, even if the blade edge takes an optimal position at the beginning of a working, the grinder action causes the blade edge to move backward, so that after a certain time it is necessary to accomplish a new forward positioning.
After all, it is clear that the different necessary adjustments and handlings are left to the operator's evaluation and to his skill and experience. Therefore, the success in a work and the time necessary for its execution depend on the operator's ability.